1. Field of the Invention
This invention relates to an optical-electronic device for detecting a charge level in a battery.
2. Description of Prior Art
Batteries are commonly used in a variety of applications requiring power including in connection with vehicles for starting, lighting, ignition and various other accessories requiring a power supply. Lead-acid batteries are commonly used in connection with vehicles and typically use lead dioxide as the positive active material and metallic lead as the negative active material, all in an electrolyte of sulfuric acid solution. As the battery progresses from charged to discharged, a specific gravity of the sulfuric acid solution decreases. Likewise, when the battery is in a highly charged state, the specific gravity of the sulfuric acid solution is correspondingly high.
The change in specific gravity of the sulfuric acid, or other electrolyte known to those having ordinary skill in the art, is used in prior art battery charge detectors such as in the device taught by Melone, U.S. Pat. No. 3,893,339. The Melone patent teaches a mechanical device wherein a colored ball floats into the focal point of a light pipe depending upon the specific gravity of the electrolyte. The output end of the light pipe thereby reflects the color of the ball when the battery is in a charged state.
However, in addition to the change in specific gravity of the electrolyte in connection with a change in charge state, the index of refraction of the electrolyte changes as well. As the battery progresses from charged to discharged, the index of refraction of the electrolyte decreases in connection with the decrease in the specific gravity. Likewise, the index of refraction increases as the battery is charged. When light is transmitted into the electrolyte, a drop in the index of refraction of the electrolyte causes a decrease of light refracted into the electrolyte.